CCAMP Working Group S. Belotti, Ed.
Internet-Draft P. Grandi
Intended status: Informational Alcatel-Lucent
Expires: February 1, 2014 D. Ceccarelli, Ed.
D. Caviglia
Ericsson
F. Zhang
D. Li
Huawei Technologies
July 31, 2013
Evaluation of existing GMPLS encoding against G.709v3 Optical Transport
Networks (OTN)
draft-ietf-ccamp-otn-g709-info-model-10
Abstract
ITU-T recommendation G.709 [G.709-2012] has introduced new fixed and
flexible Optical Data Unit (ODU) containers in Optical Transport
Networks (OTNs).
This document provides an evaluation of existing Generalized
Multiprotocol Label Switching (GMPLS) routing and signaling protocols
against the G.709 [G.709-2012] OTN networks.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 1, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
Belotti, et al. Expires February 1, 2014 [Page 1]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 20131. Introduction
GMPLS routing and signaling, as defined by [RFC4203], [RFC3473] and
[RFC4328], provides the mechanisms for basic GMPLS control of OTN
networks based on the 2001 revision of the G.709 specification. The
2012 revision of the G.709 specification, [G.709-2012], includes new
OTN features which are not supported by GMPLS.
This document provides an evaluation of exiting GMPLS signaling and
routing protocols against G.709 [G.709-2012] requirements.
Background information and a framework for the GMPLS protocol
extensions need to support [G.709-2012] is provided in [OTN-FWK].
Specific routing and signaling extensions defined in [OTN-OSPF] and
[OTN-RSVP] specifically address the gaps identified in this document.
As far as it concerns routing, analogous considerations apply to
IS-IS [RFC5307] but in the following only a gap analysis with respect
to OSPF-TE is provided.
2. G.709 Mapping and Multiplexing Capabilities
The digital OTN layered structure is comprised of digital path layer
(ODU) and digital section layer (OTU). An OTU (Optical Transport
Unit) section layer supports one ODU path layer as client and
provides monitoring capability for the OCh. An ODU path layer may
transport a heterogeneous assembly of ODU clients. Some types of
ODUs (i.e., ODU1, ODU2, ODU3, ODU4) may assume either a client or
server role within the context of a particular networking domain.
ITU-T G.872 recommendation [G.872] provides two tables defining
mapping and multiplexing capabilities of OTNs, which are reported
below.
Belotti, et al. Expires February 1, 2014 [Page 3]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 2013
this case, ODUk multiplexing may be performed prior to transport over
various rate ODU servers (as per Table 2) over associated OTU
sections.
From the perspective of multiplexing relationships, a given ODUk may
play different roles as it traverses various networking domains.
As detailed in [OTN-FWK], client ODUk connection services can be
transported over:
o Case A) one or more wavelength sub-networks connected by optical
links or
o Case B) one or more ODU links (having sub-lambda and/or lambda
bandwidth granularity)
o Case C) a mix of ODU links and wavelength sub-networks.
This document considers the TE information needed for ODU path
computation and parameters needed to be signaled for LSP setup.
The following sections list and analyze, for each type of data that
needs to be advertised and signaled, what is already there in GMPLS
and what is missing.
3. Tributary Slot Granularity
ITU-T recommendation defines two types of Tributary Slot (TS)
granularity. This TS granularity is defined per layer, meaning that
both ends of a link can select proper TS granularity differently for
each supported layer, based on the rules below:
- If both ends of a link are new cards supporting both 1.25Gbps TS
and 2.5Gbps TS, then the link will work with 1.25Gbps TS.
- If one end is a new card supporting both the 1.25Gbps and
2.5Gbps TS granularities, and the other end is an old card
supporting just the 2.5Gbps TS granularity, the link will work
with 2.5Gbps TS granularity.
3.1. Data Plane Considerations3.1.1. Payload Type and TS granularity relationship
As defined in G.709-2012 an ODUk container consist of an Optical
Payload Unit (OPUk) plus a specific ODUk Overhead (OH). OPUk OH
information is added to the OPUk information payload to create an
Belotti, et al. Expires February 1, 2014 [Page 6]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 2013
OPUk. It includes information to support the adaptation of client
signals. Within the OPUk overhead there is the payload structure
identifier (PSI) that includes the payload type (PT). The payload
type (PT) is used to indicate the composition of the OPUk signal.
When an ODUj signal is multiplexed into an ODUk, the ODUj signal is
first extended with frame alignment overhead and then mapped into an
Optical channel Data Tributary Unit (ODTU). Two different types of
ODTU are defined:
- ODTUjk ((j,k) = {(0,1), (1,2), (1,3), (2,3)}; ODTU01, ODTU12,
ODTU13 and ODTU23) in which an ODUj signal is mapped via the
Asynchronous Mapping Procedure (AMP), defined in clause 19.5 of
G.709-2012.
- ODTUk.ts ((k,ts) = (2,1..8), (3,1..32), (4,1..80)) in which a
lower order ODU (ODU0, ODU1, ODU2, ODU2e, ODU3, ODUflex) signal is
mapped via the Generic Mapping Procedure (GMP), defined in clause
19.6 of G.709-2012.
G.709-2012 introduces also a logical entity, called Optical Data
Tributary Unit Group (ODTUGk), characterizing the multiplexing of the
various ODTU. The ODTUGk is then mapped into OPUK. ODTUjk and
ODTUk.ts signals are directly time-division multiplexed into the
tributary slots of an HO OPUk.
When PT is assuming value 0x20 or 0x21,together with OPUk type (K=
1,2,3,4), it is used to discriminate two different ODU multiplex
structure ODTUGx :
- Value 0x20: supporting ODTUjk only,
- Value 0x21: supporting ODTUk.ts or ODTUk.ts and ODTUjk.
The distinction is needed for OPUk with K =2 or 3, since OPU2 and
OPU3 are able to support both the different ODU multiplex structures.
For OPU4 and OPU1, only one type of ODTUG is supported: ODTUG4 with
PT=0x21 and ODTUG1 with PT=0x20. (see table Figure 6).The
relationship between PT and TS granularity, is in the fact that the
two different ODTUGk discriminated by PT and OPUk are characterized
by two different TS granularities of the related OPUk, the former at
2.5Gbps, the latter at 1.25Gbps.
In order to complete the picture, in the PSI OH there is also the
Multiplex Structure Identifier (MSI) that provides the information on
which tributary slots the different ODTUjk or ODTUk.ts are mapped
into the related OPUk. The following figure shows how the client
traffic is multiplexed till the OPUk layer.
Belotti, et al. Expires February 1, 2014 [Page 7]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 2013
+--------+ +------------+
+----+ | !------| ODTUjk |-----Client
| | | ODTUGk | +-----.------+
| |-----| PT=0x21| .
| | | | +-----.------+
| | | |------| ODTUk.TS |-----Client
|OPUk| +--------+ +------------+
| |
| | +--------+ +------------+
| | | |------| ODTUjk |-----Client
| |-----| | +-----.------+
+----+ | ODTUGk | .
| PT=0x20| +-----.------+
| |------| ODTUjk |-----Client
+--------+ +------------+
Figure 3: OTN client multiplexing
3.1.2. Fall-back procedure
ITU-T G.798 [G.798] describes the so called PT=0x21-to-PT=0x20
interworking process that explains how two nodes with interfaces with
different PayloadType, and hence different TS granularity (1.25Gbps
vs. 2.5Gbps), can be coordinated so to permit the equipment with 1.25
TS granularity to adapt his TS allocation accordingly to the
different TS granularity (2.5Gbps) of a neighbor.
Therefore, in order to let the NE change TS granularity accordingly
to the neighbor requirements, the AUTOpayloadtype [G.798] needs to be
set. When both the neighbors (link or trail) have been configured as
structured, the payload type received in the overhead is compared to
the transmitted PT. If they are different and the transmitted
PT=0x21, the node must fallback to PT=0x20. In this case the
fallback process makes the system self-consistent and the only reason
for signaling the TS granularity is to provide the correct label
(i.e. label for PT=0x21 has twice the TS number of PT=0x20). On the
other side, if the AUTOpayloadtype is not configured, the RSVP-TE
consequent actions in case of TS mismatch need to be defined.
3.2. Control Plane considerations
When setting up an ODUj over an ODUk, it is possible to identify two
types of TS granularity, the server and the client one. The server
TS granularity is used to map an end to end ODUj onto a server ODUk
LSP or links. This parameter cannot be influenced in any way from
the ODUj LSP: ODUj LSP will be mapped on tributary slots available on
the different links/ODUk LSPs. When setting up an ODUj at a given
Belotti, et al. Expires February 1, 2014 [Page 8]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 2013
rate, the fact that it is carried over a path composed by links/
Forwarding Adjacencies(FAs) structured with 1.25Gbps or 2.5Gbps TS
granularity is completely transparent to the end to end ODUj.
The client TS granularity information is one of the parameters needed
to correctly select the adaptation towards the client layers at the
end nodes and this is the only thing that the ODUj has to guarantee.
In figure 4 an example of client and server TS granularity
utilization in a scenario with mixed [RFC4328] OTN and [G.709-2012]
OTN interfaces is shown.
ODU1-LSP
.........................................
TSG-C| |TSG-C
1.25| ODU2-H-LSP |1.25
+------------X--------------------------+
| TSG-S| |TSG-S
| 2.5| |2.5
| | ODU3-H-LSP |
| |------------X-------------|
| | |
+--+--+ +--+--+ +---+-+
| | | | +-+ +-+ | |
| A +------+ B +-----+ +***+ +-----+ Z |
| V.3 | OTU2 | V.1 |OTU3 +-+ +-+ OTU3| V.3 |
+-----+ +-----+ +-----+
... Service LSP
--- H-LSP
Figure 4: Client-Server TS granularity example
In this scenario, an ODU3 LSP is setup from node B to Z. Node B has
an old interface able to support 2.5Gbps TS granularity, hence only
client TS granularity equal to 2.5Gbps can be exported to ODU3 H-LSP
possible clients. An ODU2 LSP is setup from node A to node Z with
client TS granularity 1.25Gbps signaled and exported towards clients.
The ODU2 LSP is carried by ODU3 H-LSP from B to Z. Due to the
limitations of old node B interface, the ODU2 LSP is mapped with
2.5Gbps TS granularity over the ODU3 H-LSP. Then an ODU1 LSP is
setup from A to Z, carried by the ODU2 H-LSP and mapped over it using
a 1.25Gbps TS granularity.
What is shown in the example is that the TS granularity processing is
a per layer issue: even if the ODU3 H-LSP is created with TS
Belotti, et al. Expires February 1, 2014 [Page 9]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 2013
granularity client at 2.5Gbps, the ODU2 H-LSP must guarantee a
1.25Gbps TS granularity client. ODU3 H-LSP is eligible from ODU2 LSP
perspective since from the routing it is known that this ODU3
interface at node Z, supports an ODU2 termination exporting a TS
granularity 1.25Gbps/2.5Gbps.
The TS granularity information is needed in the routing protocol as
the ingress node (A in the previous example) needs to know if the
interfaces at the last hop can support the required TS granularity.
In case they cannot, A will compute an alternate path from itself to
Z (see figure 4).
Moreover, also TS granularity information needs to be signaled.
Consider as example the setup of an ODU3 forwarding adjacency that is
going to carry an ODU0, hence the support of 1.25Gbps TS is needed.
The information related to the TS granularity has to be carried in
the signaling to permit node C (see figure 5) choose the right one
among the different interfaces (with different TS granularitys)
towards D. In case the full ERO is provided in the signaling with
explicit interface declaration, there is no need for C to choose the
right interface towards D as it has been already decided by the
ingress node or by the PCE.
ODU3
<---------------------->
ODU0
<-------------------------------------->
| |
+--------+ +--------+ +--------+ +--------+
| | | | | | 1.25 | |
| Node | | Node | | Node +------+ Node |
| A +------+ B +------+ C | ODU3 | D |
| | ODU3 | | ODU3 | +------+ |
+--------+ 1.25 +--------+ 2.5 +--------+ 2.5 +--------+
Figure 5: TS granularity in signaling
In case an ODUk FA_LSP needs to be set up nesting another ODUj (as
depicted in figure 5), there might be the need to know the hierarchy
of nested LSPs in addition to TS granularity, to permit the
penultimate hop (i.e. C) choosing the correct interface towards the
egress node or any intermediate node (i.e. B) choosing the right
path when performing ERO expansion. This is not needed in case we
allow bundling only component links with homogeneous hierarchies. In
case of specific implementation not specifying in the ERO the last
Belotti, et al. Expires February 1, 2014 [Page 10]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 2013
granularity/PT, AMP/GMP) to enable precise path selection. In this
way, when the penultimate node (or the intermediate node performing
ERO expansion) receives such object, together with the Traffic
Parameters Object, it is possible to choose the correct interface
towards the egress node.
In conclusion both routing and signaling needs to be extended to
appropriately represent the TS granularity/PT information. Routing
needs to represent a link's TS granularity and PT capabilities as
well as the supported multiplexing hierarchy. Signaling needs to
represent the TS granularity/PT and multiplexing hierarchy encoding.
4. Tributary Port Number
[RFC4328] supports only the deprecated auto-MSI mode which assumes
that the Tributary Port Number is automatically assigned in the
transmit direction and not checked in the receive direction.
As described in [G.709-2012] and [G.798], the OPUk overhead in an
OTUk frame contains n (n = the total number of TSs of the ODUk) MSI
(Multiplex Structure Identifier) bytes (in the form of multi-frame),
each of which is used to indicate the association between tributary
port number and tributary slot of the ODUk.
The association between TPN and TS has to be configured by the
control plane and checked by the data plane on each side of the link.
(Please refer to [OTN-FWK] for further details). As a consequence,
the RSVP-TE signaling needs to be extended to support the TPN
assignment function.
5. Signal type
From a routing perspective, [RFC4203] allows advertising [RFC4328]
interfaces (single TS type) without the capability of providing
precise information about bandwidth specific allocation. For
example, in case of link bundling, dividing the unreserved bandwidth
by the MAX LSP bandwidth it is not possible to know the exact number
of LSPs at MAX LSP bandwidth size that can be set up. (see example
fig. 3)
The lack of spatial allocation heavily impacts the restoration
process, because the lack of information of free resources highly
increases the number of crank-backs affecting network convergence
time.
Moreover actual tools provided by [RFC4203] only allow advertising
Belotti, et al. Expires February 1, 2014 [Page 12]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 2013
signal types with fixed bandwidth and implicit hierarchy (e.g. SDH/
SONET networks) or variable bandwidth with no hierarchy (e.g. packet
switching networks) but do not provide the means for advertising
networks with mixed approach (e.g. ODUflex CBR and ODUflex packet).
For example, advertising ODU0 as MIN LSP bandwidth and ODU4 as MAX
LSP bandwidth it is not possible to state whether the advertised link
supports ODU4 and ODUflex or ODU4, ODU3, ODU2, ODU1, ODU0 and
ODUflex. Such ambiguity is not present in SDH networks where the
hierarchy is implicit and flexible containers like ODUFlex do not
exist. The issue could be resolved by declaring 1 ISCD for each
signal type actually supported by the link.
Supposing for example to have an equivalent ODU2 unreserved bandwidth
in a TE-link (with bundling capability) distributed on 4 ODU1, it
would be advertised via the ISCD in this way:
MAX LSP Bw: ODU1
MIN LSP Bw: ODU1
- Maximum Reservable Bandwidth (of the bundle) set to ODU2
- Unreserved Bandwidth (of the bundle) set to ODU2
In conclusion, the OSPF-TE extensions defined in [RFC4203] require a
different ISCD per signal type in order to advertise each supported
container. This motivates attempting to look for a more optimized
solution, without proliferations of the number of ISCD advertised.
Per [RFC2328], OSPF messages are directly encapsulated in IP
datagrams and depend on IP fragmentation when transmitting packets
larger than the network MTU. [RFC2328] recommends that "IP
fragmentation should be avoided whenever possible." This
recommendation further constraints solutions as OSPF does not support
any generic mechanism to fragment OSPF LSAs.
With respect to link bundling [RFC4201], the utilization of the ISCD
as it is, would not allow precise advertising of spatial bandwidth
allocation information unless using only one component link per TE
link.
On the other hand, from a signaling point of view, [RFC4328]
describes GMPLS signaling extensions to support the control for pre-
G.709-2012 OTNs. However, [RFC4328] needs to be updated because it
does not provide the means to signal all the new signal types and
related mapping and multiplexing functionalities.
Belotti, et al. Expires February 1, 2014 [Page 13]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 20136. Bit rate and tolerance
In the current traffic parameters signaling, bit rate and tolerance
are implicitly defined by the signal type. ODUflex CBR and Packet
can have variable bit rates(please refer to [OTN-FWK] table 2); hence
signaling traffic parameters need to be upgraded. With respect to
the tolerance there is no need to upgrade GMPLS protocols as a fixed
value (+/-100 ppm or +/-20ppm depending on the signal type) is
defined for each signal type.
7. Unreserved Resources
Unreserved resources need to be advertised per priority and per
signal type in order to allow the correct functioning of the
restoration process. [RFC4203] only allows advertising unreserved
resources per priority, this leads not to know how many LSPs of a
specific signal type can be restored. As example it is possible to
consider the scenario depicted in the following figure.
+------+ component link 1 +------+
| +------------------+ |
| | component link 2 | |
| N1 +------------------+ N2 |
| | component link 3 | |
| +------------------+ |
+------+ +---+--+
Figure 7: Concurrent path computation
Consider the case where a TE link is composed of 3 ODU3 component
links with 32TSs available on the first one, 24TSs on the second,
24TSs on the third and supporting ODU2 and ODU3 signal types. The
node would advertise a TE link unreserved bandwidth equal to 80 TSs
and a MAX LSP bandwidth equal to 32 TSs. In case of restoration the
network could try to restore 2 ODU3 (64TSs) in such TE-link while
only a single ODU3 can be set up and a crank-back would be
originated. In more complex network scenarios the number of crank-
backs can be much higher.
8. Maximum LSP Bandwidth
Maximum LSP bandwidth is currently advertised in the common part of
the ISCD and advertised per priority, while in OTN networks it is
only required for ODUflex advertising. This leads to a significant
Belotti, et al. Expires February 1, 2014 [Page 14]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 2013
signaling must have the possibility to setup an LSP allowing the
local selection of resources consistent with the limitations
considered during the path computation.
In figures 9 and 10 there are two examples of the need of
termination/switching capability differentiation. In both examples
all nodes only support single-stage capability. Figure 9 represents
a scenario in which a failure on link B-C forces node A to calculate
another ODU2 LSP path carrying ODU0 service along the nodes B-E-D.
As node D is a single stage capable node, it is able to extract ODU0
service only from ODU2 interface. Node A has to know that from E to
D exists an available OTU2 link from which node D can extract the
ODU0 service. This information is required in order to avoid that
the OTU3 link is considered in the path computation.
ODU0 transparently transported
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| ODU2 LSP Carrying ODU0 service |
| |'''''''''''''''''''''''''''''''''''''''''''| |
| | | |
| +----++ OTU2 +-----+ OTU2 +-----+ OTU2 ++----+ |
ODU0 | | Link | | Link | | Link | | ODU0
---->| A |_________| B |_________| C |_________| D |---->
| | | | | | | |
+-----+ +--+--+ +-----+ ++--+-+
| | |
OTU3| | |
Link| +-----+__________________| |
| | | OTU3 Link |
|____| E | |
| |_____________________|
+-----+ OTU2 Link
Figure 9: Switching and Terminating capabilities - Example 1
Figure 7 addresses the scenario in which the restoration of the ODU2
LSP (ABCD) is required. The two bundled component links between B
and E could be used, but the ODU2 over the OTU2 component link can
only be terminated and not switched. This implies that it cannot be
used to restore the ODU2 LSP (ABCD). However such ODU2 unreserved
bandwidth must be advertised since it can be used for a different
ODU2 LSP terminating on E, e.g. (FBE). Node A has to know that the
ODU2 capability on the OTU2 link can only be terminated and that the
restoration of (ABCD) can only be performed using the ODU2 bandwidth
Belotti, et al. Expires February 1, 2014 [Page 16]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 2013
With respect to the routing, please note that in case of multi stage
multiplexing hierarchy (e.g. ODU1->ODU2->ODU3), not only the ODUk/
OTUk bandwidth (ODU3) and service layer bandwidth (ODU1) are needed,
but also the intermediate one (ODU2). This is a typical case of
spatial allocation problem.
Suppose in this scenario to have the following advertisement:
Hierarchy: ODU1->ODU2->ODU3
Number of ODU1==5
The number of ODU1 suggests that it is possible to have an ODU2 FA,
but it depends on the spatial allocation of such ODU1s.
It is possible that 2 links are bundled together and 3
ODU1->ODU2->ODU3 are available on a component link and 2 on the other
one, in such a case no ODU2 FA could be set up. The advertisement of
the ODU2 is needed because in case of ODU1 spatial allocation (3+2),
the ODU2 available bandwidth would be 0 (no ODU2 FA can be created),
while in case of ODU1 spatial allocation (4+1) the ODU2 available
bandwidth would be 1 (1 ODU2 FA can be created).
What said above implies augmenting both the ISCD and the IACD.
12. Generalized Label
The ODUk label format defined in [RFC4328] could be updated to
support new signal types defined in [G.709-2012] but it would be
difficult to further enhance it to support possible new signal types.
Furthermore such label format may have scalability issues due to the
high number of labels needed when signaling large LSPs. For example,
when an ODU3 is mapped into an ODU4 with 1.25Gbps tributary slots, it
would require the utilization of thirty-one labels (31*4*8=992 bits)
to be allocated while an ODUflex into an ODU4 may need up to eighty
labels (80*4*8=2560 bits).
A new flexible and scalable ODUk label format needs to be defined.
13. Security Considerations
This document provides an evaluation of OTN requirements against
actual routing [RFC4202] and [RFC4203] and signaling mechanism
[RFC3471], [RFC3473] and [RFC4328]in GMPLS.
Belotti, et al. Expires February 1, 2014 [Page 18]

Internet-Draft GMPLS evaluation against G.709v3 OTN July 2013
New types of information to be conveyed regard OTN containers and
hierarchies and from a security standpoint this memo does not
introduce further risks with respect to the information that can be
currently conveyed via GMPLS protocols. For a general discussion on
MPLS and GMPLS-related security issues, see the MPLS/GMPLS security
framework [RFC5920].
14. IANA Considerations
This informational document does not make any requests for IANA
action.
15. Contributors
Jonathan Sadler, Tellabs
EMail: jonathan.sadler@tellabs.com
John Drake, Juniper
EMail: jdrake@juniper.net
Francesco Fondelli
Ericsson
Via Moruzzi 1
Pisa - 56100
Email: francesco.fondelli@ericsson.com
16. Acknowledgements
The authors would like to thank Lou Berger, Eve Varma and Sergio
Lanzone for their precious collaboration and review.
17. ReferencesBelotti, et al. Expires February 1, 2014 [Page 19]